Fundamentals of Transportation/Traffic

Almost anybody can build a road. Its safety and durability would likely come into question if done by an amateur, but roads are not a difficult thing to deploy. Management of these roads, however, is something that is far from simple. Safety, efficiency, and sensibility are all elements that come into play when managing a road. It is seldom possible to find a managing strategy that satisfies all three of these categories, but often a "good" strategy can be found by balancing tradeoffs. This section introduces the fundamentals of traffic management and operation, discussing everything from queueing theory to traffic signals. The discussions here cover the fundamentals for traffic operations. To this day, research is still being conducted to perfect these elements.

Contents

Queueing is the study of traffic behavior near a certain section where demand exceeds available capacity. Queues can be seen in a variety of situations and transportation systems. Its presence is one of the causes of driver delay.

Traffic Flow is the study of the movement of individual drivers and vehicles between two points and the interactions they make with one another. While traffic flow cannot be predicted with one-hundred percent certainty due to unpredictable driver behavior, drivers tend to behave within a reasonable range that can be represented mathematically. Relationships have been established between the three main traffic flow characteristics:

Shockwaves are the byproducts of traffic congestion and queueing. They are defined as transition zones between two traffic states that are dynamic, meaning they generally have the ability to move. Most drivers can identify shockwaves as the propagation of brake lights stemming from a given incident.

Traffic Signals are one of the more familiar types of traffic control. Using either a fixed or adaptive schedule, traffic signals allow certain parts of the intersection to move while forcing other parts to wait, delivering instructions to drivers through a set of colorful lights. While many benefits come with traffic signals, they also come with a series of costs, such as increasing delay during the off-peak. But, traffic signals are generally a well-accepted form of traffic control for busy intersections and continue to be deployed.

One of the basic assessments of roadway performance is by determining its Level of Service (LOS). These Levels of Service, typically ranging between A and F (A being good performance, F being poor performance), are assessed by certain predetermined thresholds for any of the three characteristics of traffic flow (flow, density, and/or velocity). Finding the correct LOS often requires reference to a table.

When computing a value of flow to determine LOS, the following formula is used:

One area of transportation operations that is still being considered is the estimation of gaps between vehicles. This is applicable in a variety of situations, primarily dealing with arrivals of vehicles at a given intersection. Gaps can only be predicted through a probability, based on several known characteristics occurring at a given time or location.

One of the more popular models used for predicting arrivals is the Poisson Model. This model is shown here: